Add the milk to a heavy-bottomed saucepan and let it come to a simmer on a medium flame. Let it continue to cook down for 20 minutes, stirring constantly.
Add the rice powder gradually, stirring constantly. Continue to stir for 5 minutes, till the rice powder is completely combined. Reduce the heat to low, and add the ghee, mawa, jaggery, and cocoa powder, and stir to combine.
Continue stirring for 8-10 minutes, then add the cardamom powder and cashew nuts. Increase flame to medium, and cook for the next 5 minutes, stirring every minute. Reduce flame to low, and cook for 5 more minutes, stirring every minute to prevent lumps.
Pour into your desired mould or bowls, and let it cool. Store in your fridge till the phirni sets.
Serve cold, topped with roughly chopped pistachios and dried rose petals.
